The invention is related to absorbent personal care products. More particularly, it concerns absorbent disposable articles such as feminine care napkins, diapers and training pants, wound care dressings and bandages, and adult incontinence products.
Personal care products typically are made with a top sheet material (also referred to as a cover sheet or liner) an absorbent core and a liquid impervious back sheet. Some may also have a surge layer or other specialized layers between the top sheet and absorbent core.
An ideal feminine care product would have no leakage and deliver comfort and discretion to the user. Current feminine care products have relatively high leakage and thus offer only modest protection to the consumer. However, a leak is rather arbitrarily defined in the art and thus consumer perceived leakage is much less. Severe leakage occurs much less frequently.
In the art, a leak is defined as menstrual discharge which stains, contacts or discolors the underwear. All leakage is categorized by three key causes: fluid does not absorb into the product, fluid is absorbed into the product but subsequently leaves it, or fluid never contacts the product. The specific reasons for this leakage may be expressed further in terms of definitive mechanisms. For instance, it may not have suitable space for absorption due to localized saturation or low contact area of the product. It may not have a suitable driving force for absorption because the pores do not have the right balance of permeability and capillarity. The interfiber spaces may be partially full of fluid. Fluid may contact the pad and run-off. The fluid may be too viscous or the pores or interfiber spaces are not large enough to allow fluid to pass.
Various product attempts have been defined to reduce leakage. For instance, wings were developed to cover the underwear and thus reduce leakage by reducing the area of the underwear that could be soiled or contacted. Others have defined emboss lines or shaping lines which cause the pad to fold in a predefined manner to concentrate fluid loading in a specific area or to increase the contact area of the pad with the body. Still others have attempted to reduce leakage by focusing on side or edge leakage presumably caused by compression of the pad by the legs thereby reducing the contact area of the target zone. These product designs have focused on keeping absorbed fluid away from the edges of the product and directing it toward the center. In many cases this is a function not only of the assembly of materials of different size and shape but also their ability to conform to and contact the body in predefined ways.
In all cases, the material systems and their concentration in a specific product design dramatically impact leakage. In the field of material systems design, leakage is a function of materials shaping and conformability as well as intake, distribution, retention and transfer.
For the purpose of this invention, intake is the absorption of body exudates over the lifetime of the product. As such it includes the initial absorption of fluid into a dry product as well as the continued uptake of that fluid into the absorbent structure. Development of superior intake systems requires an understanding of environmental conditions including the nature of the fluid and its discharge. Developing functional intake structures requires an understanding of material characteristics and their interaction with the fluid as components and systems of components including interfaces and product design. Product design includes the arrangement and geometric design of material components and their interaction with the body and fluid.
The environmental conditions surrounding the characteristics of menstrual fluid and its expulsion from the body are well understood in the art. It is this understanding which has permitted the development of suitable intake structures. Menses is a complex, heterogeneous fluid composed of plasma, red blood cells, mucin and tissue/debris. The menses simulant described in this text replicates a specific range of real menstrual fluid properties. The viscosity and elasticity of menstrual fluid span a range of 0 to 1.5 Poise and an elastic stress of 0 to 1.5 dynes/cm{circumflex over ( )}2.
It has been found that continuous flow insults in feminine hygiene products average 1 ml/hr and are not literally continuous or constant, but rather variable in rate and may even pause during a cycle. xe2x80x9cGush flowxe2x80x9d is defined as a sudden heavy flow condition and occurs at flow rates of from 0.2 to 1 ml/sec or higher. During a gush, 1-5 ml of fluid is released from the body onto the product. The term xe2x80x9ccontinuous flowxe2x80x9d is used to define any flow which falls outside of the definition of gush flow. Combining continuous and gush flow conditions results in variable flow. Essentially, xe2x80x9cvariable flowxe2x80x9d is defined as continuous flow with intermittent gush flow occurrences. The response to this problem is termed xe2x80x9cvariable flow managementxe2x80x9d and is defined as the ability to absorb and contain continuous and light flow (1-2 ml/hr) as well as multiple gushes or sudden heavy flow insults (0.5 ml/sec with a total volume of 1-5 ml) over the life of the product. In considering environmental conditions, one must also make note of the temperature, humidity, anatomy, activity, characteristics of skin and pubic hair as well as characteristics of undergarments.
Initial intake of menstrual fluid into an absorbent article is a function of the characteristics of the liner or topsheet material and the upper absorbent composite. Intake of menstrual fluid into these materials is a function of the material characteristics including the ratio of to void volume of fiber surface area, fiber orientation and fiber surface wettability. These intrinsic material characteristics specifically define the more familiar material properties of permeability, capillarity and fiber wettability which can be easily calculated and measured by techniques well known in the art. Suitable liner material characteristics are well defined in the art. These have primarily taken the form of apertured film and nonwoven covers and multi-layer composites thereof. Apertured film covers which range from structures having high permeability and low capillarity to those with high permeability and high capillarity. Nonwoven covers typically have much lower permeability with higher levels of capillarity. Regardless of the characteristics of the liner, a suitable absorbent core must be matched to it to permit fluid communication and transfer and thus good fluid intake. Both the interface between the cover and absorbent core as well as the material characteristics are important. Several researchers have defined suitable intake structures for absorption of fluids for personal care articles. For instance, Latimer et. al. (5,364,382) teaches an absorbent article having a retention and surge portion. The surge portion of the invention was defined to uptake and hold at least three successive surges of fluid and direct each to target zone and release it to the retention portion. Dodge, II et al. 20 (WO 98/22066) describes a wettable web of fibers of at most 30 microns in diameter and a permeability of 250 to 1500 Darcy""s, a capillary tension of 1.5 to 5 cm and which maintains that permeability and capillarity over the life of the web. Burnes et al. (U.S. patent application Ser. No. 09/072,172) defines an absorbent which wicks artificial menses according to a horizontal wicking test a distance of at least about 1 inch in less than about five minutes. It also denotes as a dependent claim that such fabrics have a density less than 0.15 g/cc.
Intake alone is insufficient in defining absorbency. Absorbent products must also be able to contain the body exudate in such a way as to keep the wearer comfortable and protected from fluid being expressed back onto the wearer or the undergarments. Such materials, particularly for feminine hygiene product usage, can be somewhat stiff and uncomfortable. The layers of these products are usually made from polymer fibers and films, and the absorbent core layer is usually made from wood pulp and superabsorbent particles that swell when wetted. In addition to the issue of comfort, such structures often do not allow fluid movement throughout, thus filling or overfilling the portion of the product in the area where an insult is typically delivered. Attempts have been made to address the movement of fluid in personal care products, again with the use of polymer fibers and the like.
There remains a need for a personal care product that is able to contain the body exudates in such a way as to keep the wearer comfortable and protected from fluid being expressed back onto the wearer or the undergarments. This is an object of this invention.
The objects of the invention are achieved by an absorbent system that not only takes in fluid, but then transfers that fluid further beneath the first composite. This is achieved in this invention through paired permeability, capillarity, and void volume of the first and second composites. The invention is an absorbent system composed of at least two absorbent composites that have complementary structural/surface energy characteristics. Such an absorbent system has a first absorbent Composite A which has a first permeability, a first capillarity, and a first void volume and at least one second absorbent Composite B which has a second capillarity and a second porosity multiplied by second thickness. The first absorbent Composite A is in liquid communication or contact with at least one second absorbent Composite B, such that the first absorbent Composite A, and the second absorbent Composite B have a fluid partitioning amount in Composite A, a third triple intake time (IT3) and a rewet value. Note that capillarity is measured in units of centimeters of saline as described in the test methods section below.
It is preferred that Composite A have a capillarity which is less than 7.8, a void volume which is not less than 0.09 cc/cm2 and not more than 0.51 cc/cm2 and a permeability greater than 150 darcies, that Composite B have a porosity multiplied by thickness greater than 2.1, hat the difference in capillarity between Composite A and B (CTB-CTA) be greater than 1, that the fluid partitioning amount in Composite A be less than about 22 percent, the third triple intake time be less than 40 seconds and rewet value be less than 0.28 grams.
The invention also pertains to the use of these absorbent systems in absorbent articles for personal care or wound care to promote rapid acquisition and retention of viscous or viscoelastic fluids while providing comfort and dryness to the user by transporting fluid away from the user""s skin.